Comprehensive studies with delta-9-Tetrahydrocannabinol for induced mutagenic activity in rodents has indicated no measurable effects. The procedures that were conducted to determine mutagenic activity included cytogenetic procedures utilizing both micronuclei and metaphase analyses; dominant lethal studies: host-mediated studies, and blood and urine analysis of treated mice. Additionally no mutagenic activity was found when the drug was evaluated directly against the histidine auxotrophs of S. typhimurium in the presence or absence of microsomal enzymes derived from liver homogenates.